BackgroundConcern thattrans-fatty acids formed in the partial hydrogenation of vegetable oils may increase the risk of coronary disease has existed for several decades, but direct evidence on this relation in humans is limited.Methods and ResultsWith a case-control design, we studied the association between intake oftrans-fatty acids and a first acute myocardial infarction among 239 patients admitted to one of six hospitals in the Boston area and 282 population control subjects. Intake of trans-fatty acids was estimated using a previously validated food frequency questionnaire. After adjustment for age, sex, and energy intake, intake of trans-fatty acids was directly related to risk of myocardial infarction (relative risk for highest compared with lowest quintile, 2.44; 95% confidence interval, 1.42, 4.19; for trendP< .0001). This relation remained highly significant after adjustment for established coronary risk factors, multivitamin use, and intake of saturated fat, monounsaturated fat, linoleic acid, dietary cholesterol, vitamins E and C, carotene, and fiber. Intake of margarine-–the major source oftrans-isomers– was significantly associated with risk of myocardial infarction.ConclusionsThese data support the hypothesis that intake of partially hydrogenated vegetable oils may contribute to the risk of myocardial infarction.